Wireless systems may use an Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme. The IEEE 802.11a/g standards describe OFDM systems and the protocols used by such systems. In an OFDM system, a data stream is split into multiple substreams, each of which is sent over a subcarrier frequency (also referred to as a “tone”). One of the advantages of OFDM systems is their ability to provide a low arithmetical complexity equalization scheme for frequency selective channels (also known as the multipath effect). The equalization is reduced in the frequency domain after demodulation by a FFT (Fast Fourier Transform) to scalar multiplications, one for each tone. This feature enables OFDM systems to use a relatively simple channel equalization method, which is essentially a one-tap multiplier for each tone.
Despite these advantages, OFDM transmissions, like other wireless transmissions, are susceptible to the effects of residual carrier offsets, phase noise, and quadrature imbalance effects. These impairments cause inter-carrier interference (ICI), which can degrade system performance. These impairments also affect the accuracy of channel estimates, which when used for channel equalization, add a secondary, but not insignificant, degradation to the quality of the equalized signals.